The present invention relates to a milk liner for a milk liner assembly of an animal milking system, and in particular, though not limited to a milking system for milking cows. The invention also relates to a milk liner assembly, as well as to a milking cluster for use in a milking system, and the invention relates to a method for minimising excessive radial inward contraction, during milking of an animal, of a teat engaging flange of a milk liner onto a teat of an animal passing therethrough.
Milk liner assemblies for use in milking systems for milking cows are provided in groups of four which are commonly referred to as a milking cluster. Each milk liner assembly of the cluster is provided for engaging one of the teats extending downwardly from a cow's udder. The milk liner assembly comprises an outer shell, typically of stainless steel, within which is located a milk liner of a resilient flexible synthetic rubber material. The milk liner forms a teat receiving cavity for receiving a teat from the cow's udder. One end of the milk liner terminates in a teat engaging flange which defines a teat accommodating opening for accommodating the teat of the cow's udder into the teat receiving cavity. The other end of the milk liner terminates in an outlet port to which a milking vacuum is applied for drawing milk from the teat receiving cavity, which has been expressed from the cow's teat. The milk liner forms with the outer shell an annular vacuum chamber which extends around the milk liner, and to which a pulsating vacuum is applied. The pulsating vacuum applied to the annular vacuum chamber co-operates with the vacuum applied to the teat receiving cavity for pulsing the milk liner into tight radial engagement with the teat in the teat receiving cavity for massaging the teat during milking.
One problem with such milk liner assemblies is that during periods of no vacuum in the annular vacuum chamber around the milk liner between vacuum pulses during each pulsating vacuum cycle, when the milk liner is tightly urged into engagement with the teat, the milking vacuum applied to the teat receiving cavity tends to draw the teat into the teat receiving cavity, thus causing the milk liner to creep along the teat towards the cow's udder. This causes serious problems during milking, particularly when the milk liner assembly has crept along the teat to the extent that the teat engaging flange at the end of the milk liner commences to engage the cricoid fold at the root of the teat where it extends from the udder. On engagement of the cricoid fold the teat engaging flange contracts around the cricoid fold, thus closing off the supply of milk from the udder to the teat. This, thus, may prevent further milking of the cow from the teat, and in general, prevents a cow being completely milked.
In order to prevent creeping of the milk liner, and in turn the milk liner assembly along a teat, it is known to increase the weight of the milking cluster. Since milking clusters depend downwardly from the cow's udder, the increase in weight urges the milk liner assemblies, and in turn the milk liners downwardly against the action of the milking vacuum, thereby to some extent preventing creep of the milk liner upwardly along the teat. However, increasing the weight of a milking cluster is undesirable, since firstly, there is no guarantee that the extra increase in weight will be sufficient for preventing creep of the milk liner along the teat, and secondly, the extra weight of the milking cluster militates against efficient milking, particularly where a large number of cows are to be milked, since the extra weight reduces the speed at which the milking clusters can be attached to and detached from the teats of the cows. An alternative method for preventing creep along the teat is to empirically match the diameter of the teat accommodating opening defined by the teat engaging flange of the milk liner to the teat size of the herd. This, in general, is impractical.
There is therefore a need for a milk liner which overcomes the problem of creep of a milk liner along a teat to which the milk liner is attached.